linux-kernel - Re: [PATCH] cciss: Ignore stale commands after reboot

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Date:	Thu, 2 Jul 2009 11:18:54 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Hannes Reinecke <hare@...e.de>
Cc:	scameron@...rdog.cca.cpqcorp.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cciss: Ignore stale commands after reboot

On Thu, Jul 02 2009, Hannes Reinecke wrote:
> Jens Axboe wrote:
> > On Thu, Jul 02 2009, Hannes Reinecke wrote:
> >> When doing an unexpected shutdown like kexec the cciss
> >> firmware might still have some commands in flight, which
> >> it is trying to complete.
> >> The driver is doing it's best on resetting the HBA,
> >> but sadly there's a firmware issue causing the firmware
> >> _not_ to abort or drop old commands.
> >> So the firmware will send us commands which we haven't
> >> accounted for, causing the driver to panic.
> >>
> >> With this patch we're just ignoring these commands as
> >> there is nothing we could be doing with them anyway.
> >>
> >> Signed-off-by: Hannes Reinecke <hare@...e.de>
> >> ---
> >>  drivers/block/cciss.c     |   14 ++++++++++++--
> >>  drivers/block/cciss_cmd.h |    1 +
> >>  2 files changed, 13 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
> >> index c7a527c..8dd4c0d 100644
> >> --- a/drivers/block/cciss.c
> >> +++ b/drivers/block/cciss.c
> >> @@ -226,7 +226,16 @@ static inline void addQ(struct hlist_head *list, CommandList_struct *c)
> >>
> >>  static inline void removeQ(CommandList_struct *c)
> >>  {
> >> -	if (WARN_ON(hlist_unhashed(&c->list)))
> >> +	/*
> >> +	 * After kexec/dump some commands might still
> >> +	 * be in flight, which the firmware will try
> >> +	 * to complete. Resetting the firmware doesn't work
> >> +	 * with old fw revisions, so we have to mark
> >> +	 * them off as 'stale' to prevent the driver from
> >> +	 * falling over.
> >> +	 */
> >> +	if (unlikely(hlist_unhashed(&c->list))) {
> >> +		c->cmd_type = CMD_MSG_STALE;
> >>  		return;
> >>
> >>       hlist_del_init(&c->list);
> >
> > Ehm, that looks rather dangerous. What's the level of testing this patch
> > received?
> >
> Where is the danger here?

The danger is that the patch doesn't even compile :-)
At least it had the { at the end of the if, otherwise it would have been
insta-hang.


> 
> With the original code we would be issuing a warning
> and return.
> But then we hit this codepath:
> 
>  	while (!hlist_empty(&h->cmpQ)) {
>  		c = hlist_entry(h->cmpQ.first, CommandList_struct, list);
>  		removeQ(c);
> 		c->err_info->CommandStatus = CMD_HARDWARE_ERR;
> 
> and the driver goes boom as c->err_info is not initialized.
> 
> This frequently happens if you're trying to do a kdump
> while the system is doing I/O.
> If you object to the removed WARN() I can easily put this
> in, but without the fix there is a good chance that
> kdump fails on cciss machines.
> 
> And note we can't do anything with the stale commands anyway,
> as the context having sent the commands originally is long gone.
> 
> Cheers,
> 
> Hannes
> --
> Dr. Hannes Reinecke		      zSeries & Storage
> hare@...e.de			      +49 911 74053 688
> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
> GF: Markus Rex, HRB 16746 (AG Nürnberg)

-- 
Jens Axboe

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